Remember in this difficult time, there are only 2 ways dealing with COVID:

Bad and worse ones. This is the former:

Transfer all international inbound flights to hainan. Quicken vaccination there.

Loose in, tight out.

Foreign visitors with either vaccination or negative tests can immediately see their same status Chinese contacts there, from mainland. No mask, little restriction, put faith on island geography, vaccine, hot and humid air there.

After certain time say 2-3 weeks, with negative test they can visit mainland ,maybe be isolated further a bit when arriving.

Hainan economy would be super hot, Airbnb hotels will be needed.

Sounds radical? Well, this pandemic already causedlots of unthinkables , and more will follow. china has to gradually open up no matter what, this is the least painful and crazy way.

Land border control? Tell incomers they may immediately see their contacts in hainan, or face long inconvenience at border hotels. China border seems long, but large parts have minimal difficulty, such as Tibet, Yalu river or xinjiang. Russia or Mongolia ones not too difficult either. challenges are south. Mobilizing civilians to monitor is the only choice, yes, I am talking the biggest weapon china be able to suppresses COVID so far:

Grandma/pas with red arm bands.